Radiation beam forming apparatus



Jan. 3, 1967 A. D. LE VANTINE 3,295,432

7 RADIATION BEAM FORMING APPARATUS Filed Aug. 13. 1962 4 Sheets-Sheet l RELLHWVE \NTENSVYY 12. {A 3. 18

A ALAN 0. L E VANT/NE INVENTOR Jan. 3, 1967 A. D. LE VANTINE 3,296,432

RADIATION BEAM FORMING APPARATUS Filed Aug. 13, 1962 4 Sheets-Sheet 2 TARGET OBJECT 58A 4 40A 5PAQN6 f WRROR ,AMRROR I?H\l6 MIRROR Q I '7 A INVENTOR.

ALLAN 0. LE l/ANT/NE A 7TORNEY A. D. LE VANTINE RADIATION BEAM FORMING APPARATUS Jan. 3, 1967 4 SheetsSheet :5

Filed Aug. 13, 1962 ALLAN 0. LE VANTINE INVENTOR.

ATTORNEY Jan. 3, 1967 A. D. LE VANTINE 3,296,432

RADIATION BEAM FORMING APPARATUS Filed Aug. 13, 1962 4 Sheets-Sheet 4 FOCUS OF OFFAX\E PARABQLA BEAM SHAVER \NTEN sm v 4 CONT ROLLER COLLIMATION ANGLE ALLA/V 0. AEl/AA/r/NE INVENTOR.

A FOR/V5) United States Patent 3,296,432 RADIATION BEAM FORMING APPARATUS Allan 1). Le Vantine, Tarzana, Califi, assignor, by mesne assignments, to TRW, Inc., a corporation of Ohio Filed Aug. 13, 1962, Ser. No. 216,677 3 Claims. (Cl. 240-413) The present invention relates to high intensity light sources and more particularly to improved arrangements for providing a beam of radiation having a spectral distribution substantially corresponding to that of the sun and having a substantially uniform field intensity.

For many purposes it is desirable that a beam of radiation be provided in which all of the ray directed to an object to be illuminated are substantially parallel. While that objective is not particularly formidable in the ordinary case, it becomes considerably more difficult to achieve when requirements of high efliciency, high intensity, and uniform field illumination are added.

While it should be understood that the present invention is not limited to any specific application, it may be most conveniently and understandably described by reference to one particular embodiment useful for producing a beam of radiation similar to sunlight for irr-adiative testing of aircraft and the like. Our sun impresses approximately fourteen hundred watts of power on each square meter of the surface of the earth facing it. To duplicate that energy on an area of about eighty square feet, for example, would require over ten thousand watts of radiant power. Because of the inherent low efficiency of practically all devices for converting electrical energy to light, the production of such magnitudes of light power having spectral distributions comparable to sunlight requires nearly one hundred kilowatts of electrical power. To additionally provide that all the rays are collimated within about two degrees requires a substantial advancement of the prior art known to applicant.

Accordingly, it is a primary object of the present invention to provide a sunlight simulation apparatus which produces a beam of radiation having collimation characteristics approximately like that of the suns ray and producing substantially uniform light intensity at all elemental portions of a predetermined illuminated area.

It is another object of the present invention to provide an apparatus capable of producing a beam of radiation having a spectral energy distribution approximating that of the sun, a substantially uniform intensity over an area of at least several square feet, and a degree of ray collimation comparable to that of sunlight.

It is further object of the present invention to provide an apparatus for generating a beam of radiation substantially simliar to the solar radiation which is encountered by an object outside the earths atmosphere.

It is a general object of the present invention to provide an improved apparatus for producing a high intensity, uniform energy beam of radiation including components in the visible and ultraviolet wavelength ranges,

In accordance with the preferred embodiment of the present invention, an apparatus for simulating high altitude environmental conditions includes a large vacuum chamber, adapted to receive an object which is to be subjected to thermal testing, and an apparatus associated with that vacuum chamber for applying a beam of radiation similar to sunlight to the object. Preferably, the means for generating light is disposed externally of the vacuum chamber and transmits a beam of light througha transparent window member in one wall of the chamber for impingement of the beam on the test object by way of a parabolic reflector contained within the chamber. The radiation source apparatus preferably comprises a carbon arc lamp and a reflective means placed behind the positive carbon of the lamp to collect a major portion of the 3,296,432 Patented Jan. 3, 1967 radiation emanating therefrom and to direct that radiation along the light path to the test object. In order to achieve optimum uniformity of the light intensity across the area to be illuminated, the light collecting means which is positioned adjacent the carbon are preferably comprises a plurality of concentrically arranged, annular reflective surfaces of different mean diameters. The different annular surfaces are differently spaced from the carbon are in a manner such that the radial distances from the carbon arc to the mean diameter of each reflective surface are substantially equal.

The foregoing and other objects and features of the present invention will be apparent from the following description taken with the accompanying drawing, throughout which like reference characters indicate like parts, which drawing forms a part of this application and in which:

FIGURES la and lb are optical diagrams useful in explaining the problem to which the present invention is directed;

FIGURE 2 is a schematic optical diagram of a multi- -surface reflective means which forms a part of the present invention;

FIGURE 3 is a schematic diagram of a radiation generating and projecting system in accordance with the present invention;

FIGURE 4 is an exploded cross-sectional view of a multisurface reflector assembly of the present invention;

FIGURE 5 is a plan view partially cut away of a vacuum chamber for receiving an object to be irradiatively tested;

FIGURE 6 is a cross-sectional view taken along the lines 6-6 of FIGURE 5; and

FIGURE 7 is an optical system diagram illustrating structural and operational features of the apparatus shown in FIGURES 5 and 6.

In apparatus for simulating the effects of sunlight, it is necessary to irradiate a test object with light having a spectral distribution generally similar to that of the sun over the wavelength range from 0.2 to 3.6 microns. The light beam must also have uniform intensity at every point of impingement on the target area. The apparatus of the present invention provides uniform field intensity, excellent spectral distribution, and a higher efficiency than any comparable prior art system known to applicant. In order to duplicate the thermal effects of the sun in a laboratory of limited space, critical attention must be given to the problems of collimating the rays of light from the source and achieving uniformity of light intensity across the area to be illuminated. Applicant has found that the most efficient means for converting electrical power to light energy with a spectral distribution reasonably comparable to sunlight is a conventional carbon arc lamp of the general type commonly utilized in moving picture projectors and the like. Applicant has found that the spectral distribution produced by a carbon arc lamp utilizing carbon electrodes to which appropriate salts have been added and operating at approximately seventy-seven volts and one hundred sixty amperes will produce light energy across the wavelength range from 0.2 microns to 3.6 microns with the energy distribution being a close approximation of the solar spectral distribution outside of the' earths atmosphere. The efficiency of a carbon arc lamp using 13.6 millimeter high intensity carbon electrodes is approximately thirty-four percent. The radiation is emitted in an angular distribution which represents a cardiode of revolution of a radius vector is used to denote radiation intensity. An elliptical reflector positioned concentrically about the positive electrode and behind the arc crater will collect energy from a solid angle of about one hundred forty degrees and, therefore, can capture about seventy-nine percent of the radiation emanating from the electric arc. In FIGURE 1A there is shown diagrammatically an optical system comprising a radiation source 12 representative of the high temperature plasma of a carbon arc, and a conventional elliptical reflector 10 disposed concentrically about an axis 11 which extends through the center of the reflector 10, the source 12, and the center of an area 20 which is to be illuminated. The diameter of the radiation source is indicated at 19. Light emanating from the source 12 and reflected from a single point 21 on a surface of the reflector has a dispersion pattern as indicated by the central ray 14 and the limiting rays 16 and 18. The area 6 over which the light is dispersed at the second focal plane 20 is indicated by the numeral 22. From FIGURE 1a it will be appreciated that the diameter of dispersion 6 at the second focal plane 20 is directly proportional to the diameter 5 of the source, is directly proportional to the distance from the particular reflective point 21 to the second focal plane 20 and is inversely proportional to the distance from the source 12 to the particular reflective point 21. If a conventional elliptical reflector 10 were to be used with a source 12 of finite diameter, the rays reflected from points near the center of the elliptical reflector 10 would be dispersed over a larger area at the second focal plane 20 because of the fact that the radial distance r from the source 12 to the reflector 10 is smaller at points near the center of the elliptical reflector 10. That is, since 5 is inversely proportional to the radial distance r of the reflector 10 from source 12, the dispersion pattern produced at the second focal plane 20 decreases as rays reflected from points further from the center of the elliptical reflector 10 are considered. This means that if a conventional elliptical reflector 10 were used, and assuming a lambert source, a nonuniform field of light would be produced at the second focal plane 20 with the relative intensity varying substantially as shown by the curve 24 in FIGURE 112. That effect, of course, is to be avoided since a primary object of an apparatus for simulating sunlight is to achieve uniform intensity across the area to be illuminated.

In accordance with the present invention, applicant overcomes the foregoing difliculty by utilizing a multisurface light collecting means 27 as shown diagrammatically in FIGURE 2. The light collecting means 27 comprises three annular segments 36, 38, and 40 which are positioned concentrically aboutthe axis 11 and with the planes of their mean circumferences being normal to the axis 11. The reflective surface 36 which has the minimum transaxial diameter is positioned a maximum distance r along the axis 11 from the source 12. The next larger diameter reflective surface 38 is positioned an axial distance from the source 12 such that the mean radial distance r of the reflective surface 38 is equal to the mean radial distance r,, from the source 12 to the first reflective surface 36. The third reflective surface 40 is positioned a still lesser axial distance from the source 12 so that its mean radial distance r from the source substantially is equal to the mean radial distance r and 7 By this arrangement, rays reflected from the mean diameter points of the three reflective surfaces are caused to form dispersion patterns of the same diameter at the second focal plane F That is, in accordance with the equation by holding the radial distance r "-=*r Er Er from the source 12 to each one of the reflectors 36, 38 and 40 substantially equal, the different dispersion patterns 5 at the second focal plane 20 (FIGURE 2), are held substantially the same. It can also be seen from FIGURES 1 and 2 that at the second focal plane 20, all rays converge to form a least common circle. The field intensity across this least common circle is approximately uniform because the source to reflector radius for each ray is substantially the same length as the same radius for every other ray (i.e., r zr r The dispersion at the second focal plane 20 is nearly the same for all rays directed to the second focal plane 20 by the multisurface light collecting means 27. Ideally, the reflective surfaces 36, 38, and 40 are separate segments of a family of elliptical curves having the same foci F and F The shape of these reflective surfaces 36, 38, and 40 can best be understood by first considering the geometrical construction of a spheroid or ellipsoid of revolution. A prolate ellipsoid of revolution is defined by Websters New International Dictionary, Second Edition, Unabridged, as being a solid figure generated by revolution of an ellipse about its major or transverse axis. If we consider that a segment is cut from such an ellipsoid, along a plane normal to the major axis, it may be appreciated that an annular segment is formed. As shown in FIGURE 2, the lamp comprises three such annular elliptical segments. The three ellipses from which the three reflectors are taken are members of the same family of ellipses in that they all have the same foci F and F The segments preferably are formed or chosen so that the inner diameter of the larger reflector 40 is approximately equal to the outer diameter of the intermediate reflective surface 38, and so that the inner diameter of reflector 38 is approximately equal to the outer diameter of reflector 36.

While the multisurface reflective means has been described above as preferably comprising a plurality of annular sections of different ellipsoids of revolution, it should be understood that the separate annular reflective surfaces need not conform exactly to the curvature of an ellipse. In practice when a plurality of segments are used, each of which has a width along the major axis 11 of approximately one tenth of its mean diameter, the surfaces do not need to be precisely elliptical but may be circular conic sections having an angulation such that the surfaces correspond respectively to chords of the elliptical sections 36, 38, and 40 as shown in FIGURE 2. The essential feature of the light collecting means 27 is that the different segments 36, 38, and 40, whether elliptically curved or whether conic sections, are spaced longitudinally along the axis 11 in a manner such that the radial distances r r and r from the source 12 to the mean diameters of the segments 36, 38, and 40 are approximately equal.

In FIGURE 3 there is illustrated an optical projection system in accordance with the present invention embodying a multisurface reflective means 27 which comprises three segments 36, 38, and 40, each of which may be machined from an aluminum alloy plate having a thickness of about two and one-fourth inches and a diameter of about seventeen inches. The reflector elements 38, and 40 are spaced apart by a spacing ring 42 which is provided with an externally peripheral mounting ring or shoulder 41 which may be appropriately bolted or otherwise secured to conventional support arrangements (not shown). The reflector elements 36, 38, and 40 may be peripherally bolted together and supported from the support ring 42. The positive carbon electrode 30 is supported from an electrode feed mechanism 26 which is shown in block diagram form. Mechanisms for feeding carbon electrodes to the lamp assembly are, per se, well known in the art and need not be described in detail. A similar electrode feed mechanism 28 is disposed at one side of the axis 11 and supports a negative carbon electrode 32 in a position to extend adjacent the end of the axially aligned positive electrode 30 so that a carbon are 34 may be established and supported between the negative electrode 32 and the positive electrode 30. The negative electrode support and feed mechanism 28 is likewise conventional. The rate of electrode feed provided by the electrode feed mechanisms 26 and 28 may, if desired, be controlled by a servomechanism or feedback circuit electric arc 34 impinges upon the preferably elliptical in ternal surfaces of the members 36, 38, and 42 and is reflected therefrom to form a beam 44 extending from the lamp assembly to a parabolic light reflecting member 50 which may be used to fold and collimate the beam when it is desired to contain the complete system within a limited laboratory space. The light beam 44 between the lamp assembly and the mirror or reflecting member 50 is concentric with the axis 11. By providing a parabolic reflecting surface on the member 50, the rays are collimated so that the beam 52 between the reflecting member 50 and the object 54 consists of substantially parallel rays. In a preferred embodiment of the invention, the collimation of the light beam 52 is within one and one-half degrees. For control of the beam intensity, a variable diameter iris or beam stop, represented schematically by elements 46 and 48, may be interposed peripherally about the light beam 44 between the arc lamp assembly and the parabolic reflecting member 50 at the second focal point F Because of the dispersion technique which is utilized, the variable diameter iris comprising elements 46 and 48 does not reduce the diameters of the beam 52 falling on the target object 54 but rather the iris operates to continuously vary the uniform radiation intensity from a maximum corresponding to the maximum energy output of the multisurface light collecting means to zero intensity when the variable diameter iris is fully closed.

FIGURE 4 shows an exploded view of the multisurface reflective means 27 comprising the first, second, and third reflective members 36, 38, and 40 and the support member 42. The manner in which the members 36 through 42 are to be assembled together may be readily appreciated from a consideration of FIGURE 4. It will be understood that FIGURE 4 is a cross section taken along the central axis of the multisurface reflective means 27 of FIGURE 3, and that each of the elements 36 through 42 is a figure of revolution about that axis so that the reflective surfaces 36A, 38A, and 40A are segments of different prolate ellipsoids of revolution. As stated heretofore, the surfaces 36A, 38A, and 40A need not be perfectly elliptical but may be in a practical structure closely approximated by circular sections having substantially the same curvature of the elliptical section. In one preferred embodiment of the present invention which has been constructed, the abovementioned components preferably have the following dimensions:

Inches Member 36O.D. 14.75

Member 36I.D. 2.58 Member 36Reflective Surface O.D 12.0 Member 38O.D. 16.0

Member 38I.D. 9.875 Member 38Reflective Surface O.D 14.5

Member 40O.D. 18 Member 40I.D. 14.1 Member 42O.D. 17.125

Member 42I.D. 13.125

FIGURES 5 and 6 illustrate incorporation of the optical system of FIGURE 3 in a practical arrangement for irradiating a test object 60 which is contained within a cryogenic vacuum chamber 55. The vacuum chamber 55 comprises a cylindrical tank having a peripheral outer wall 57, upper and lower closures 56 and 58, respectively, and an inner liner which is cooled in a conventional manner by liquid nitrogen tubes distributed thereon. A test object 60 as shown in FIGURE 5 may be supported within the vacuum tank 55, preferably with the supports being arranged to permit rotation of the test object about a horizontal axis (i.e., an axis normal to the longitudinal axis of the cylinder). Supported interiorly of the vacuum tank 55 adjacent one side wall portion thereof is a pair of parabolic light reflecting members 62 and 64 optically corresponding to the parabolic reflecting member 50 shown in FIGURE 3. The members 62 and 64 should each have an area large enough to intercept and reflect the entire light beam 44 emanating from a lamp assembly 27'. The light beam 44 projected from the lamp or beam source 27' enters the vacuum chamber 55 through a port arrangement comprising a positive lens 68 which is supported on an angularly disposed portion 66 of the tank wall and is secured thereto by means of a vacuum tight sealing arrangement comprising a conventional O-ring 70 and a clamping ring 72. In projection systems for simulation of sunlight within a cryogenic vacuum chamber as illustrated by FIGURES 4, 5, and 6, it is not necessary to comply with the rigorous specifications of usual optical systems because there is no requirement for high resolution or freedom from aberrations. For reflective surfaces such as the internal surfaces of members 36, 38, and 40, (FIGURE 3) continuity of the reflective surface is important. The surface must not have small pits or imperfections which would reduce the reflectance below that normally considered acceptable for an optical reflector. However, large dimension unevennes of the surface is not detrimental. Unevenness will result in a loss in resultion; but so long as it does not reduce the efliciency of the surface of as a reflector or grossly deteriorate the light collecting function, such unevenness is not objectionable. Likewise, in the systems of the present invention, coma and curvature of field are not objectionable so long as the desired degree of incident energy flux at the object 54 is achieved. Similar considerations hold for retracting elements; some amount of chromatic aberration is not objectionable. As long as the chromatic aberration does not seriously reduce the intensity of the ultraviolet energy in the beam, such abberation may be acceptable. The foregoing considerations enable construction of systems in accordance with the present invention without strict adherence to usual optical concepts. Thus, large reflecting and refracting elements of simple and economical construction may be used. The multisurface elliptical light collecting means 27 (FIGURES 3 and 4) can be machined from soft materials such as aluminum alloy. The large parabolic reflectors 62 and 64 (FIGURE 6) can be inexpensively formed from ordinary plate glass by the simple sag-molding process or may be formed from sheet aluminum by screwing a polished sheet of aluminum to supports having the desired parabolic curvature. Critical accuracy in the grinding of the vacuum chamber port lens 68 is not essential.

The foregoing freedom from the usually rigorous design criteria encountered in optics does not extend to all aspects of the apparatus of the present invention. The high power levels which are present in the optical systems of apparatus in accordance with the present invention dictate that all reflective and transmissive elements must have a reasonably high efficiency. Also, the requirement of very accurately diuplicating the spectral distribution of sunlight makes it necessary to choose optical elements which have very uniform transmission efiiciencies over the wavelength range from 0.2 to 3.6 microns. The optical system of the apparatus of FIG- URES 5 and 6 employs only a single light transmissive element, i.e., the vacuum chamber port lens 68. For the lens 68, a high purity, fused quartz material having a high efficiency of light transmission in the ultraviolet range is most desirable. Of the materials known to applicant, a fused quartz sold under the trade name Suprasil, by Amersil Quartz Division of Englehard Industries, Inc., 1111 Wilshire Boulevard, Los Angeles, California, has the best transmission characteristic in the ultraviolet range. While Suprasil is the best material from the efficiency standpoint, it is extremely expensive and diflicult to obtain in quantity and, hence, is perhaps somewhat impractical for use in more economical systems. Other high purity, high fused quartz materials which applicant has used are General Electric Type and Corning 7940 U.V. grade, which are almost identical and are readily obtainable at reasonable cost. These materials have very satisfactory transmission characteristics.

An additional consideration in the use of optical elements is the equilibrium temperature at which they will operate in an optical system which transmits light power of several kilowatts.

When the apparatus of FIGURES and 6 utilizes the optical system illustrated by FIGURE 3, the vacuum chamber window lens 68 may, if desired, be a planar fused quartz window. Alternatively, various arrangements may be constructed in which the chamber window lens 68 functions additionally as a refractive component in the optical system diagram. FIGURE 7 diagrammatically illustrates one such alternative embodiment of the present invention which may be structurally similar to the arrangement shown in FIGURES 5 and 6 but which differs in that the multisurface light collecting means 27 is constructed and arranged to have a second focal point at a plane 73. This short focal length light collecting means comprising elements 36', 38, and 40' enables reduction of the collected light to a least common circle at the second focal plane 73 so that the light beam may be passed into the vacuum chamber 56 through a chamber port lens 63' of minimum diameter. Rays emanating from the reflective elements 36, 38', and 40 are refracted by the postive lens 68' and are directed to an off-axis parabola 64 corresponding to the parabolic reflectors 62 and 64 of FIGURE 6. The off-axis parabola 64, of course, i designed to have a parabolic curvature sufficient to collimate the intercepted rays into a beam having the required collimation angle of one and one-half degrees. As shown in FIGURE 7, the para bolic reflector 64' intercepts the light rays transmitted by the positively refracting chamber port lens 68 and directs those rays to impingement on the surface of the target or object member 60. In addition to enabling use of a small diameter chamber port 68', the optical system illustrated by FIGURE 7 additionally enables control of the beam intensity by means of an intensity controlling, variable diameter iris 46 disposed peripherally around the beam path between the multisurface light collector 27 and the chamber port 68'. In addition, since the radiation beam is reduced to a least common circle at the second focal plane 73, the shape of the beam may be determined by provision of beam shaping members 74 around the beam at the second focal plane 73. The beam shaping members 74 may be fixed screens for cutting off undesired peripheral portions of the beam or may be variable for adjusting the diameter or dimensions of the area to be illuminated. Moreover, the beam shapers 74 may be constructed and arranged to provide a rectangular or hexagonal or other shape of beam, as desired. As stated heretofore, the chamber port lens 68 of the embodiment shown in FIG- URES 5 and 6 in its simplest form comprises a planar, non-refracting quartz window. With such a window using the optical system illustrated in FIGURE 3, the apparatus has a relative long focal length. For some applications, the long focal length may be somewhat undesirable. In such cases, the focal length of the optical system illustrated in FIGURE 3 can be considerably shortened without changing the overall effect of the system by utilizing a negative or Barlow lens for the light transmitting chamber port 68 of FIGURE 6. Such a negative lens serves to extend the apparent focal length of the light collecting means 27 and thereby enables reduction of the beam to a least common circle at the object to be illuminated with a substantially reduced overall optical path length. Since a vacuum tight chamber port is, in any event, necessary, the interposition of a negatively refracting lens in the optical path, which lens performs the dual function of transmitting the light through the atmospheric-vacuum interface, does not reduce the overall efficiency of the optical path.

While the present invention has been illustrated and described with reference to certain preferred embodiments only, it will be obvious to those skilled in the art that it is not so limited but is susceptible of various changes and modifications without departing from the spirit and scope thereof.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows 1. In an apparatus for simulating high altitude environmental conditions:

a vacuum chamber adapted to receive an object to be tested;

a high intensity radiation source disposed externally of said chamber and adapted to approximately duplicate the spectral distribution of sunlight;

a radiation transparent window member disposed in one wall of said chamber and forming a portion of a radiation path from said source to said object;

multisurface reflective means positioned to receive radiation from said source for directing a beam along a predetermined axis to illuminate said object; and

said reflective means comprising a plurality of substantially annular reflective surfaces of different mean diameters disposed concentrically about said axis with each of said surfaces lying in a different plane substantially normal to said axis and with said different planes being spaced along said axis so that different ones of said surfaces are substantially equidistant from said radiation source,

said annular reflective surfaces having a width substantially smaller than the straight line distance from the radiation source to said annular reflective surfaces,

said plurality of substantially annular reflective surfaces having a substantially common focal point,

said radiation source being positioned substantially in said substantially common focal point.

2. A light source:

a target member to be illuminated by radiation derived from said source;

a light path extending from said source and including at least one portion having a central axis which extends through said source;

a light collecting means disposed adjacent said source for gathering a substantial portion of the light emanating therefrom and directing the same along said path to provide substantially uniform flux density over a predetermined area at said target member, said means comprising at least two separate reflective surfaces with each of said surfaces being symmetrically disposed relative to said axis; and

each of said surfaces having a radial cross section which substantially corresponds to a segment of one ellipse of a family of ellipses having the same foci, and with all said surfaces being spaced at approximately the same radial distance from said source so that the different light paths from said source to said target by way of different ones of said surfaces are all substantially the same length and so that the light from said source is substantially uniformly distributed over a predetermined area of said target member,

said reflective surfaces having a width substantially less than the radial distance from said source to said reflective surfaces,

said radial distance from said source to said surface being the distance from said source to a median point in said width of each said reflective surfaces.

3. A light source:

a target member to be illuminated by radiation derived from said source;

a light path extending from said source and including at least one portion having a central axis which extends through said source;

a light collecting means disposed adjacent said source 9 10 for gathering a substantial portion of the light em- References Cited by the Examiner anating therefrom and directing the same along said UNITED STATES PATENTS path to provide substantially uniform flux density over a predetermined area at said target member, 1,421,506 7/ 1922 lf 24O46-41 said means comprising at least two separate reflec- 1,694,067 12/1928 LeWlS 2 1 tive surfaces with each of said surfaces being sym- 1,864,696 6/1932 Steel et al. c 88-24 metrically disposed relative to said axis; 2,716,183 8/1955 Stebbins 240-4135 each of said surface having a radial cross section 3,064,364 11/1962 Schueller.

which substantially corresponds to a segment of a 3,078,760 2/1963 Brownscombe 240-41.35 X dicerent one of a plurality of elliptical curves With all said elliptical curves having the same foci and FOREIGN PATENTS with all said surfaces being spaced at approximately 772 04 4 1934 France,

the same radial distance from said source so that the different light paths from said source to said OTHER REFERENCES targe/t by Way of different ones of said Surfaces are 15 Jenkins: Fundamentals of Optics, Published 1950 all substantially the same length and the llght from (New York) page 32 relied upon Said Source 13 Sl.1bStant1a11y umf.Orm1y distributed Tenney Engineering, Incorporated, pamphlet, received over a predetermined area of said target member, in the Patent Ofiice August 31, 1961 p g P g 2 and an off-axis parabola displosed in the light path interfelled upon) mediate the source and the target member, said reflective surfaces having a width substantially NORTON ANSHER Pnmary Exammerless than the radial distance from said source to said BENJAMIN BORCHELT, Examiner reflective surfaces, said radial distance from said source to said surface p CHANDLER, CHARLES C, LOGAN, 11

being the distance from said source to a median Assistant Examinem point in said width of each said reflective surfaces. 

1. IN AN APPARATUS FOR SIMULATING HIGH ALTITUDE ENVIRONMENTAL CONDITIONS: A VACUUM CHAMBER ADAPTED TO RECEIVE AN OBJECT TO BE TESTED; A HIGH INTENSITY RADIATION SOURCE DISPOSED EXTERNALLY OF SAID CHAMBER AND ADAPTED TO APPROXIMATELY DUPLICATE THE SPECTRAL DISTRIBUTION OF SUNLIGHT; A RADIATION TRANSPARENT WINDOW MEMBER DISPOSED IN ONE WALL OF SAID CHAMBER AND FORMING A PORTION OF A RADIATION PATH FROM SAID SOURCE TO SAID OBJECT; MULTISURFACE REFLECTIVE MEANS POSITIONED TO RECEIVE RADIATION FROM SAID SOURCE FOR DIRECTING A BEAM ALONG A PREDETERMINED AXIS TO ILLUMINATE SAID OBJECT; AND SAID REFLECTIVE MEANS COMPRISING A PLURALITY OF SUBSTANTIALLY ANNULAR REFLECTIVE SURFACES OF DIFFERENT MEANS DIAMETERS DISPOSED CONCENTRICALLY ABOUT SAID AXIS WITH EACH OF SAID SURFACES LYING IN A DIFFERENT PLANE SUBSTANTIALLY NORMAL TO SAID AXIS AND WITH SAID DIFFERENT PLANES BEING SPACED ALONG SAID AXIS SO THAT DIFFERENT ONES OF SAID SURFACES ARE SUBSTANTIALLY EQUIDISTANT FROM SAID RADIATION SOURCE, SAID ANNULAR REFLECTIVE SURFACES HAVING A WIDTH SUB- FROM STANTIALLY SMALLER THAN THE STRAIGHT LINE DISTANCE FROM THE RADIATION SOURCE TO SAID ANNULAR REFLECTIVE SURFACES, SAID PLURALITY OF SUBSTANTIALLY ANNULAR REFLECTIVE SURFACES HAVING A SUBSTANTIALLY COMMON FOCAL POINT, SAID RADIATION SOURCE BEING POSITIONED SUBSTANTIALLY IN SAID SUBSTANTIALLY COMMON FOCAL POINT. 